On La Silla, ESO operates two major telescopes (3.6-m telescope, New Technology Telescope (NTT). They are equipped with state of the art instruments either built completely by ESO or by external consortia, with substantial contribution by ESO.

APEX, the Atacama Pathfinder Experiment, is a collaboration between Max Planck Institut für Radioastronomie (MPIfR), Onsala Space Observatory (OSO), and the European Organisation for Astronomical Reseach in the Southern Hemiphere (ESO). APEX has a suite of heterodyne spectrometers and wide-field bolometer cameras operating in most of the atmospheric windows from 0.2 to 1.4 mm.